Oncolytic viruses in cancer therapy

Abstract

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature's own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.

Fig. 1

Impediments to virotherapy. This schematic drawing represents a tumor mass, and highlighted are some of the known and putative problems oncolytic viruses are facing. Oncolysis is ongoing in the nodule to the left, whereas tumor destruction is almost complete in the nodules to the right. At the top, a new nodule has formed consisting of virus-resistant cells emerging under the selective pressure of oncolysis. Tumor cells may also avoid viral destruction by hiding within strands of connective tissue.

Fig. 2

Two hypothetical outcomes of virotherapy. In the upper panel, due to the highlighted problems the therapy will ultimately fail using virus infection alone. Several strategies have therefore been proposed to enhance treatment efficacy in order to achieve complete eradication of the cancer (lower panel). Finding a combination resulting in optimal treatment regimen will probably become increasingly important in the future.